Index OO See NKVD OPD, 814 See also Marshall, George C Open city, 814, 849 Operational art, 315, 462, 814, 956, 1062, 1169 Operational group, 814 Operational ready rate, 814 Operational research See Science research Operations See Operational art Opium trade See Imperial Japanese Army; Sino-Japanese War (1937–1945) Opolchentsy, 138, 749, 815, 901, 996, 1063, 1106, 1146 See also Leningrad, siege of; Mozhaisk Line; Smolensk; TAIFUN Oppenheimer, J Robert (1904–1967) See Nuclear weapons programs Oradour-sur-Glane ( June 10, 1944), 698, 815 – 16, 921, 1153 Order #227, 170, 816, 842, 1037 Order #270 See Desertion Ordnungspolizei, 816, 960 Orel-Bolkhov offensive operation ( January 7–February 18, 1942), 816 – 17, 949, 1008 Orel-Briansk offensive operation (February 25–March 23, 1943), 422, 649, 679, 745, 817, 902, 904, 927 Origins of World War II See Absolute National Defense Sphere; Abyssinian War; Anglo-German Naval Agreement; Anti-Comintern Pact; Anti-Semitism; Appeasement; Autarky; Axis alliance; Chamberlain, Neville; Chinese Civil War (1927–1949); Churchill, Winston; Collective security; Danzig; Emperor cult; Fascism; Finnish-Soviet War (1939–1940); Genro; Geopolitik; Germany; Great Depression; Greater East Asia Co-Prosperity Sphere; Guandong Army; Hitler, Adolf; Hokushin; Imperial Japanese Army; Imperial Japanese Navy; Issekikai; Italy; Japan; Jieshi, Jiang; Kodo-ha; Kokubo kokkai; Kokutai; League of Nations; Lebensraum; Manchuria; MarcoPolo Bridge incident; Mukden incident; Munich Conference; Mussolini, Benito; Mutilated victory; Nanshin; Nazism; Nazi-Soviet Pact; Neutrality Acts; Nomonhan; Pact of Steel; Pearl Harbor; Polish corridor; Rhineland; Roosevelt, Franklin; Sino-Japanese War (1937–1945); Spanish Civil War (1936– 1939); Stalin, Josef; Stresa Front; Sudetenland; Tosui-ken; Tripartite Pact; Vernichtungskrieg; Versailles, Treaty of; Volksdeutsch; individual countries and leaders Orpo See Ordnungspolizei Oscar, 818 OSMBON, 18, 789, 905 Osoaviakhim, 684, 818 OSS See Office of Strategic Services (OSS) Ostarbeiter, 437, 818, 916 See also Smersh Ostashkov-Pochep Line, 139, 819, 1062 Ostheer See Heer; OKH; OKW; Wehrmacht Ostland See Reichskommissariat Ostland Ostlegionen, 819 See also Osttruppen Ostmark, 819 Ostministerium, 819 Osttruppen, 288, 289, 314, 819 – 20, 870, 916, 995, 1009 See also Cossacks; D-Day ( June 6, 1944); Hiwis; Ostlegionen; Repatriation; Russian Liberation Army (ROA); Smersh; Vlasovites Ostwall, 383, 820, 1079, 1188 OTTO (1936), 820 OTTO (1940), 820 OVERLORD ( June 6–August 19, 1944), 158, 194, 206, 220, 236, 243, 246, 251, 262, 268, 279, 288, 289, 308, 342, 394, 396, 420, 454, 458, 468, 820 – 21 See also Air Defence of Great Britain (ADGB); Atlantic Wall; BAGRATION; Belgian Gate; Bigoted; Bradley, Omar; Dieppe Raid; E-boats; EPSOM; Falaise pocket; Festung Europa; Force Franỗaise de l’Intérieur (FFI); FUSAG; GOODWOOD; Hodges, Courtney; Irish Free State; Patton, George; Résistance (French); Rommel, Erwin; Rundstedt, Gerd von; additional entries throughout the encyclopedia Ozawa, Jizaburo (1886–1966), 672, 821 – 22, 850 Pacific War (1941–1945), 227, 229, 472, 823 – 25, 1116 See also ABDA command; Admiralty Islands; Alamo Force; Australia; Balikpapan; Biak; Biological weapons; Bismarck Archipelago; Bismarck Sea, Battle of; Blamey, Thomas; Bougainville; CARTWHEEL; Fletcher, Frank; Fugo; Fukuryu; Germany first 1297